Three former division commanders of the Immigration Bureau (IB) have taken bribes for approving visas for more than 3,325 Chinese nationals, according to former politician and massage parlour tycoon Chuwit Kamolvisit.

The approvals of these non-immigrant visas -- Type B (Business) and Type O (Other purposes) -- were made between 2020 and last year by the three police major-generals, Mr Chuwit said on Wednesday.

Two of them, identified by Mr Chuwit only by the initials of their first names K and D, are former classmates of deputy national police chief Pol Gen Surachate Hakparn at the Royal Police Cadet Academy, he claimed.

He identified the other as "N", claiming this is the initial of his first name.

All three served as chiefs of the IB's Divisions 4 and 5, said Mr Chuwit.

"Since Pol Maj Gen K and Pol Maj Gen D, who signed to approve these visa-switching applications for the Chinese nationals, are Pol Gen Surachate's classmates, I was wondering if he would ever dare take action against them," Mr Chuwit asked.

According to him, the cost of getting such an application approved by the three former commanders ranged from 100,000-300,000 baht per person.

Chinese nationals arrived in Thailand on a tourist visa which allowed them to stay for 30 days.

During that time they sought to have their visas changed to a Type B or Type O with the help of the Chinese criminal syndicate being investigated independently in connection with the drug trade and other illegal activities, said Mr Chuwit.

A Chinese legal firm was set up to assist them, he said, adding the Khon Kaen-based Prans Hanyu Foundation was also involved in the racket.